Caption: Sand grains. Coloured scanning electron micrograph (SEM) of rounded grains of sand. Sand is composed largely of the mineral quartz, and has particles which range in size from 0. 06 to 2 millimetres in diameter. Sand from desert regions, which is windblown, tends to be more rounded than marine sand, which is shaped by water movement. Magnification: x25 at 6x7cm size. x40 at 4x5"